1 Field of the Invention
The present invention relates to an apparatus for displaying information signal of a specimen obtained by bombarding it with an accelerated electron beam in a form of an image representing various characteristics of the specimen on a cathode ray tube adapted to perform the scanning operation in synchronization with the bombarding electron beam.
2. Description of the Prior Art
It is known that, when a specimen is two-dimensionally scanned with an accelerated primary electron beam, secondary electrons, X-rays and cathode fluorescence are produced in dependence on the characteristics or inherent properties of the specimen. Further, the quantity of the primary electrons absorbed by the specimen as well as that of electrons passing through the specimen will vary depending on the individual specimens as employed. It is possible to visually observe various characteristics of the specimen by displaying the information of the secondary electrons, X-rays and cathode fluorescence as well as absorption or transmission of the primary electrons (which is hereinafter called specimen information) on a face plate of a cathode ray tube (hereinafter termed also simply CRT) in a form of visible image.
In order to produce a specimen image of a high quality, the primary electron beam must of course be properly focussed on the surface of the specimen. Besides, when information obtained from the specimen surface is amplified and then used to display an image of specimen on CRT, it is required to perform adjustments of contrast and brightness of the displayed image. Such adjustments have been heretofore made by observing the displayed image itself, and therefore a high skill is required to perform the adjustments for a relatively short time.
Accordingly, it will mean a great contribution in the art if an apparatus is available which allows a display of a wave form representing the information of focussing, contrast and brightness of the image concurrently with the display of the image of specimen on one and the same cathode ray tube to thereby facilitate the adjustments of the above parameters for a short time with the aid of the displayed waveform.
In this case, it is very important to simultaneously display on the same CRT the wave form for adjustments and the image of specimen. In other words, the quality of the image as displayed may possibly be varied to a great extend even by a fine adjustment of the contrast, brightness or the like. It is thus required to carry out the fine adjustment by observing the specimen image and the wave form for adjustment at the same time.